Capacitive Angular Position Sensor with RFID Remote Reading
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Solution Overview
Problem
Existing non-contact angular position sensing mechanisms for rotatable parts in meters face challenges with high power consumption and low precision, especially in hostile environments, and often suffer from interference issues due to the proximity of electrodes in electrostatic capacity-based systems.
Innovation Solution
A capacitive coupling system with two relatively rotatable parts, each having working surfaces that form pairs for sensing and coupling purposes, where transmitting electrodes on one part and a receiving electrode on the other part allow for angular position detection without the need for batteries or wires, using radio frequency identification (RFID) technology for remote reading.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If electrostatic capacity-based sensing is used, then angular position detection is achieved, but interference occurs due to electrode proximity
Solution Approach 1:
The patent transitions from planar electrode arrangements to three-dimensional spherical electrode configurations. The transmitting electrode and receiving electrode are positioned on opposite sides of a spherical surface, utilizing the third dimension to maximize separation distance while maintaining detection capability. This spatial arrangement eliminates interference between electrodes while preserving angular position measurement accuracy.
2Measurement precision
If drive coil with LC resonant circuit is used, then angular position sensing is achieved, but significant power is consumed
Solution Approach 1:
The patent employs passive capacitive coupling where the receiving electrode naturally couples with the transmitting electrode through the dielectric medium without requiring active power consumption. The system uses the inherent electrical properties of the materials and geometry to achieve sensing, eliminating the need for powered resonant circuits or drive coils.
3Device complexity
If electrodes are positioned adjacently on the same disk, then device complexity is reduced, but output signal contains noise
Solution Approach 1:
The patent moves from two-dimensional planar electrode positioning to three-dimensional spherical positioning. By placing transmitting and receiving electrodes on opposite sides of a sphere, the design achieves maximum separation in three-dimensional space, eliminating noise from adjacent electrode interaction while maintaining a single-disk simple structure.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The system achieves low noise and low power consumption while providing high precision angular position measurement, is easy to manufacture, and allows for remote monitoring of meter dials without the need for external power sources, enhancing reliability in harsh environments.
Implementation Method 1
The capacitive coupling between the receiving electrode and the transmitting electrode dependents on the relative angular positions of the two relative rotatable parts
Implementation Method 2
a coupling electrode is secured to the coupling surface of the rotating part; the coupling electrode connected to the receiving electrode electrically for transferring the signals thereon
Data Source
AI summary
A visually and remotely readable apparatus is provided which comprises a plurality of sensing units, a control unit and a flexible printed cable (FPC) to connect two units for exchanging information therebetween. A preferable structure of the sensing unit includes a fixed part secured to the body of the apparatus and two oppositely positioned rotatable parts, where two rotatable parts mounted on a common shaft with the fixed part arranged therebetween forming two angular position sensors. Each sensor is based on the capacitive coupling between two working surfaces of the rotatable part and the respective working surfaces of the fixed part with the electrodes are secured thereto. Two working surfaces of one part are confronted with two respective working surfaces of another part forming two working surface pair. Each sensor has two working surface pairs, one working surface pair is sensing pair for sensing angular position; another is coupling pair for coupling sensing signals. A plurality of transmitting electrodes are secured to the working surface of the sensing pair of the fixed part; a receiving electrode is secured to the working surface of the sensing pair of the rotatable part; an output electrodes is secured to the working surface of the coupling pair of the fixed part; a coupling electrode connected to the receiving electrode is secured to the working surface of the coupling pair of the rotatable part. To each of the plurality of the transmitting electrodes is applied a respective one of polyphase squarewave voltages. The capacitive coupling between the electrodes of the sensing pair is dependent on the relative positions of two rotatable part, and the output signal voltages on the output electrode which coupled from the coupling electrode represents the angular position of the rotatable part. In the first embodiment provided for the sensors, the shape of working surfaces is in a conical frustum; the second embodiment, the shape of working surfaces is a cylinder; the third embodiment, the shape of working surfaces is a disc; the fourth embodiment, with a cylinder-shaped working surface and a disk-shaped working surface, is a combination of the second and the third embodiments provided as an example of the application of the embodiments. A circuit of the control unit is provided for processing data, generating control signals for the sensors. By using radio frequency identification (RFID) technique to exchange information with the reader station outside of the apparatus and power the system are also disclosed in the invention.